Laminates and laminated tubes and packages for hard-to-hold products having volatile components

ABSTRACT

Sheet materials and packages made therefrom, and capable of holding hard-to-hold products such as methyl salicylate and other volatile components, in one form include a foil layer (12) and a layer (14) of EVOH between foil layer (12) and the enclosed product. A carboxy-modified adhesive layer (18) is disposed between the EVOH layer (14) and the product. Additional layers (28, 30, 32, 34, 36, 38, 40) are used in the sheet material for purposes of adhesion, appearance, protection, body, and the like. A coextruded film structure comprises an EVOH layer (514), a surface layer (516), an intervening adhesive layer (518), and a fourth covering layer (519) for covering and protecting the EVOH layer (514), especially from physical abuse. Packages made from the sheet materials and coextruded film can be in the form of sachets, pouches and bags, or in the form of dispensing tubes.

This application is a continuation-in-part of application Ser. No.07/132,833 filed Dec. 14, 1987 now pending.

BACKGROUND OF THE INVENTION

This invention pertains to laminated sheet materials used for packaging.Such sheet materials are commonly known for their use in making bags,pouches, and tubes. The sheet materials of the invention can be used formaking any of these types of packages. This particular description willbe addressed primarily to the discussion of the sheet materials as theyrelate to packaging products in lap seamed tubes.

Laminated sheet materials of the variety disclosed herein, andespecially those containing a layer of metal foil, have been used forpackaging such materials as toothpaste, foods, and certain chemicalcompounds. There remain certain products which have not heretofore beenpackaged in multiple layer sheet materials of the type disclosed in theinvention because of the package's susceptibility to being chemicallyattacked by the contained product. Particularly troublesome, andaddressing now the problem addressed by the inventors herein, are thosecompounds which use especially volatile, and chemically active,materials such as methyl salicylate.

Conventional sheet materials of the type disclosed in this inventioncontain a barrier layer of aluminum foil, and protective, covering,sealing, bonding, and the like layers of polymeric materials on bothsides of the aluminum foil. It has been found unsatisfactory to packageproducts containing methyl salicylate in known sheet materials of thistype because methyl salicylate penetrates through the interveningpolymeric layers and attacks the interfacial adhesion on the productside of the metal foil layer. The attack on the metal foil interfacialadhesion is effective to cause delamination of the sheet material, andsubsequent failure of the package.

There are a number of advantages to the laminated type of sheet materialof the invention over the otherwise conventionally used packages ofmetal foil. The conventional tubes of metal foil, which are used forpackaging these hard-to-hold products, have a number of disadantages.Among the disadvantages are the thickness of the metal foil which isused, and its associated tendency to crack upon repeated flexing. Metalfoil tubes are also more expensive. While such disadvantages have beenknown for quite some time, there has not, in the past, been asatisfactory substitute material for use in packaging the materialsaddressed by the inventions herein.

Thus it would be highly desirable to find a functionally acceptablematerial which can be used to package materials which attack the moreconventional multiple layer sheet materials which are used in packagesof this type.

It is an object of this invention to provide multiple layer sheetmaterials capable of holding such a volatile material as methylsalicylate in combination with a metal foil which provides a highbarrier to the transmission of product components through the packagewall.

It is another object of the invention to provide a multiple layer sheetmaterial which is capable of holding certain volatile materials, withoutdelaminating, over the typical life of the product.

It is still another object of the invention to provide a multiple layersheet material which is capable of holding products containing methylsalicylate and similar materials for the expected shelf life of theproduct without significant loss of any of the volatile components, andthe resulting change in the product composition.

SUMMARY OF THE INVENTION

A preferred embodiment of the invention is seen in a sheet materialwhich comprises at least five layers. The first layer is comprised of ametal foil, preferably aluminum foil, having a first primed surface anda second surface opposite the first primed surface. A second layer ofethylene vinyl alcohol has a first surface disposed toward the firstfoil layer and a second surface disposed away from the foil layer. Athird adhesive means between the first and second layers adheres thosefirst and second layers to each other. A fourth protective layer isdisposed on the second surface of the first foil layer, to provideprotection of the foil from physical abuse. A fifth covering layer isdisposed on the second surface of the second layer of ethylene vinylalcohol. Preferably the fifth layer is composed of a heat sealablepolymer such as linear low density polyethylene. Linear low densitypolyethylene is a copolymer of ethylene and an α-olefin containing atleast three carbon atoms, and is available from, for example, DowChemical Company.

The third adhesive means comprises one or more layers of material whichare capable of bonding the first layer of foil to the second layer ofethylene vinyl alcohol. The adhesive means preferably comprises fourseparate components. The first component is a layer of ethylene acrylicacid adhered to the first surface of the foil layer through a secondcomponent of a primer containing a chromium complexed polyacrylic acid.The second component primer comprises the surface priming on the firstlayer of metal foil. The third component is an anhydride modifiedpolymer containing an olefinic base resin such as a polyethylene or apolyethylene copolymer, especially linear low density polyethylene. Thethird component of the adhesive means is bonded to the first surface ofthe EVOH layer. The fourth component of the preferred adhesive means isa layer of low density polyethylene disposed between the olefinicadhesive on the EVOH and the EAA.

A sixth layer of adhesive is preferably disposed between the second andfifth layers of the sheet material. The olefinic adhesive layer betweenthe second ethylene vinyl alcohol layer and the low density polyethylenelayer of the third adhesive means can be considered a seventh layer ofthe sheet material.

In preferred embodiments, the overall thickness of the sheet material isbetween 0.1 and 0.6 mm.

With respect to the ethylene vinyl alcohol of the second layer, it ispreferred that the vinyl alcohol component comprises 55 mole percent to72 mole percent vinyl alcohol moieties, most preferably 60 mole percentto 64 mole percent. If the alcohol content is below the preferred range,the barrier to transmission of a volatile component such as methylsalicylate is reduced such that the layer of ethylene vinyl alcoholrequired to provide an equivalent barrier is undesirably thickened inorder to provide the necessary level of total barrier to the methylsalicylate transmission. If the vinyl alcohol component is increasedabove the preferred range, the extrusive properties of the ethylenevinyl alcohol copolymer are negatively affected to the point that theextrusion process becomes difficult. Also the adhesive capabilities ofthe EVOH layer may be negatively affected by increased amount of alcoholin the EVOH layer. Additionally, the ethylene vinyl alcohol layer may beundesirably brittle.

It is preferred that the fifth covering layer be polymeric and that thesixth adhesive layer between the second ethylene vinyl alcohol layer andthe fifth covering layer comprise a base polymeric resin, preferably anolefin resin, and anhydride comprising active anhydride componentequivalent to between about 0.10% and about 0.60% by weight maleicanhydride. Preferably, the anhydride modification is between 0.26% and0.40% (equivalent) of the weight of the composition, and most preferablybetween 0.30% and 0.36% of the overall weight of the composition of theadhesive polymer. It is preferred that the composition of the sixthadhesive layer have a melt index at 210° C. of between 3 and 9,preferably between 5 and 7. Further, in some cases the sixth layer mayinclude, in addition to the base resin and the anhydride component, upto 15%, preferably up to 10%, of an elastomeric material.

It is preferred that the polymeric composition of the fifth layer andthe base resin of the sixth layer both comprise linear low densitypolyethylene copolymers.

In preferred embodiments of the invention, the composition of theseventh layer comprises the composition of the sixth layer.

Another aspect of the sheet materials of the invention comprisesessentially a five layer coextruded film containing outer surface layersof low density polyethylene and linear low density polyethylene, a corelayer of ethylene vinyl alcohol, and adhesive layers, on either side ofthe ethylene vinyl alcohol layer, intervening between the ethylene vinylalcohol and the respective surface layers. The five layer sheet materialof this embodiment corresponds essentially to five layers on thepreviously recited embodiment which contains the metal foil. Those fivelayers are the five outermost layers of the sheet material, which fivelayers include the surface layer of linear low density polyethylene. Thesame parameters and limitations as described above apply to the fivelayer sheet material. That sheet material may be made, and preferably ismade, by a coextrusion process.

Any of the sheet materials of the invention, including the five layersheet material, and the more complex sheet structure containing metalfoil, may be used to make packages for containing chemically activeproducts, and especially active products having components having a highlevel of chemical activity in combination with the high level ofvolatility of at least one component.

The sheet materials of the invention include a sheet materialcomprising, from the inside surface thereof in the package outwardly afirst layer of a polyolefin; a second adhesive layer comprising apolyethylene and about 0.10% to about 0.60%, preferably about 0.26% toabout 0.40% (equivalent) of an anhydride, and having a melt index at210° C. of between 3 and 9; and a third layer of ethylene vinyl alcohol,the packaing sheet material being functional to retard transmission ofthe volatile component of, for example, methyl salicylate, acetone,acetic anhydride, undecylenic acid, ichthamnol coal tar derivative, orpolyurethane prepolymer, through the sheet material, sufficient toprovide for acceptable compositional stability of the volatile componentin the product over the normal shelf life of the product. Thecomposition of the first layer may, in some cases, be based onpropylene. In other cases, it may be based on ethylene. Further, it maybe based on a combination of ethylene and propylene. Preferably itcomprises a copolymer of ethylene and up to 10% of an alpha olefin,having a carbon chain at least three carbon atoms long, and commonlyreferred to as linear low density polyethylene.

The invention includes the method of making a package which comprisesfabricating the sheet material by adhering a first layer of a coveringto a second layer of metal foil, and on the surface of the foil oppositethe first layer, adhering, by use of intervening adhesive means, acoextruded film structure comprising 3 or more layers and including aheat sealable layer on the surface thereof opposite the foil layer, thecoextruded film structure being between 0.05 mm and 0.25 mm thick. Themethod further comprises fabricating the sheet material into a packageenclosure by forming a tube comprising a lap seal, and with one end ofthe tube open. The method further comprises placing a product in thepackage and closing and sealing the one end to complete the fabrication,filling, and sealing of the package. The method is especiallyadvantageous where the product contains a component capable of attackingthe metal foil layer and wherein the coextruded film structure includesa layer of ethylene vinyl alcohol comprising at least about 55% vinylalcohol, and no more than about 72% vinyl alcohol, and an adhesive layeron one surface of the ethylene vinyl alcohol layer. The adhesive layercomprises polyethylene as a base resin and about 0.10% to about 0.60%,preferably about 0.26% to about 0.40% anhydride (equivalent), theadhesive layer having a melt index, at 210° C., of between 3 and 9.

In fabrication of typical packages, portions of the sheet material arefolded onto each other in a tubular configuration in formation of a lapseam, wherein an upper surface of an underlying layer is in facingcontact with a lower surface of an overlying layer. A seal is fabricatedby means of heating the sheet materials such that the upper surface ofthe underlying layer is bonded to the lower surface of the overlyinglayer.

In another construction useful in making packages of sheet material ofthe invention, the same general container shape may be fabricated usingfin seals wherein portions of the same surface are brought into facingcontact with each other to make the closure seals.

In still other cases, the sheet material of the invention may be used incombination with other sheet structures to fabricate less than theentire package structure. In these cases, the sheet material of theinvention is typically seen as a closure, cover, or other type of lidmaterial which is bonded to a second, and different packaging sheetmaterial, such as a preformed rigid tray.

Another way of considering the invention is that it provides, in twolayers, one of ethylene vinyl alcohol and the other of the anhydridemodified polyethylene composition, preferably linear low densitypolyethylene, a composite barrier structure capable of holding productshaving one or more of the recited hard-to-hold components.

The thus made packages of the invention are entirely satisfactory, andare preferred, for packaging products having volatile components.Especially the packages made with the sheet structures containing themetal foil layer are desirably used for packaging products which have,in their composition, components which exhibit both the properties ofhigh levels of chemical reactivity and high levels of volatility, orwhich are sensitive to exposure to light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of a sheet material characteristic of theinvention.

FIG. 1A shows a cross-section of a prior art sheet structure.

FIG. 2 shows a side-view of a typical tube package made with the sheetmaterials of the invention.

FIG. 3 is a cross-section of a tube of the invention taken at 3--3 ofFIG. 2.

FIG. 4 is a cross-section of a typical fin-sealed package of theinvention.

FIG. 5 is a cross-section of a less complex multiple layer film of theinvention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Referring to FIG. 1, there is seen a cross-section of sheet material 10representative of the sheet materials of the invention. With respect topreventing the transmission of volatile product components through thepackaging sheet material, it is important in some embodiments to providea layer of metal foil 12 which serves as a barrier to transmission ofmany components. The interfacial adhesion on the product side of metalfoil 12, however, is susceptible to being attacked by the morechemically aggressive components of some of the materials which may bepackaged. Thus it is important in some cases to provide protectivematerials between the metal foil layer 12 and that interior surface ofthe package which is in contact with the product.

With respect to protecting the interfacial adhesion at metal foil layer12, there is provided, in the FIG. 1 embodiment, a layer 14 of ethylenevinyl alcohol (EVOH), a layer 16 of linear low density polyethylene(LLDPE) on the surface of the sheet material, and a layer 18, betweenlayers 14 and 16, of an adhesive polymer having a base resin of linearlow density polyethylene and an anhydride modification.

Between the EVOH layer 14 and foil layer 12, there is provided a secondadhesive layer 20, an adhesive layer 22 of ethylene acrylic acid (EAA)or ethylene methacrylic acid (EMAA), and a layer 24 of low densitypolyethylene (LDPE) interposed between layers 20 and 22. A chromiumcomplexed primer, shown as layer 26 between foil layer 12 and layer 22improves the adhesion between the foil and layer 22. A second layer 28of EAA or EMAA is on the other surface of foil layer 12, and serves as abonding site for the adjacent layer 30 of LDPE.

Layer 32 of LDPE is on the outside surface of the sheet material, andlayer 34 of pigmented low density polyethylene is adjacent layer 32.Layer 36 of paper is bonded to LDPE layers 30 and 34 by primer, shown aslayers 38 and 40, of polyethylene imine (PEI) primer.

FIG. 2 shows a tube package 42 made with the sheet material 10 of theinvention. Sheet material 10 is used especially to make the sidewalls 44of the tube. The sidewall 44, made from sheet material 10, is used incombination with the head 46 and the cap 48 in fabrication of the tubepackage.

FIG. 3 shows a cross-section of the tube of FIG. 2; and especially showsthe typical method of joining the edges of the sheet material infabricating the lap seam 50 which is formed along the length of the tubein joining the two edges of the sheet material to each other. FIG. 3also shows the positioning of the packaging sheet material 10 of thetube relative to the product 52 contained therein.

FIG. 4 shows a cross-section of an alternate construction of packages ofthe invention. In the construction illustrated in FIG. 4, the closure offacing elements of the packaging material is made by means of fin seals54, rather than by lap seals as at 50 in the tube of FIG. 3.

While the embodiments shown in FIGS. 1-4 are characteristic of thepreferred embodiments of the invention, there is also seen to be noveltyand utility in a simpler depiction of the invention as shown in thesheet structure of FIG. 5. With respect to the numbering of FIG. 5, thelast two digits of the layer numbers in FIG. 5 correspond to the twodigit numbers given for similar layers in FIG. 1. Thus layer 514 isEVOH. Layer 516 is LLDPE. Layer 518 is an adhesive comprising a baseresin of LLDPE and an anhydride modifier. Layer 519 is a covering layerover layer 514, and is provided primarily for the purpose of physicallyprotecting the EVOH in layer 514, though layer 519 may also serve otherfunctions as well.

Returning now to FIG. 1, and a detailed discussion of how each of thelayers participates in the functioning of the sheet materials andpackages of the invention. As stated earlier, the objective of theinvention is to provide sheet materials and packaging which are capableof successfully holding aggressive products, and especially those whichhave volatile and chemically active components. An especially hard tohold material is methyl salicylate. As a starting point directed towardsolving the problem of packaging products containing methyl salicylate,the prior art sheet material shown in FIG. 1A was used to package aproduct containing methyl salicylate. As shown by the labeling of thelayers in FIGS. 1 and 1A, the prior art sheet material of FIG. 1A wasidentical to the upper layers of FIG. 1 of the instant invention.Specifically, the layers common to both FIG. 1 and FIG. 1A are layers12, 22, 26, 28, 30, 32, 34, 36, 38 and 40. When a methyl salicylateproduct was packaged in tubes made from sheet materials of FIG. 1A, thesheet material showed attack at the foil interface, evidenced bydelamination of the sheet material, resulting in failure of the packageto hold the product.

It appeared that the failure of the package was related to attack on theinterfacial adhesion between foil layer 12 and EAA layer 22/primer 26.Thus began the search for a means to protect the foil interface fromattack by the methyl salicylate. After substantial amount of testing andevaluation, it was discovered that a single layer film of EVOH providedwhat appeared to be an acceptable barrier to the transmission of methylsalicylate. And thus began the attempt by the applicant herein toincorporate the EVOH into the sheet material in such a way that the foilinterface would be protected from attack by the methyl salicylate. Tothat end, experimental sheet materials were made incorporating the EVOHinto the sheet material.

While respect to the layers between foil layer 12 and the outside layer32 of the sheet material, there is no particular criticality to thesequence or composition of those layers in obtaining the foil-protectingbarrier properties important to the sheet material herein. Thatcomposite of layers is shown with respect to its preferred structure.Rather, the structuring of the sheet material on that outer side of foillayer 12 is independent of the structuring with respect to providing thebarrier function for protecting foil layer 12 from attack by theproduct. Those outer layers serve such purposes as protecting foil layer12 from physical abuse from outside the package, for providing bulk orbody to the film, for graphics, color, etc., and other means foreffecting the appearance of the package. Thus their selection is made bythe sheet material designer independent of the objective of protectingthe foil interface from attack by chemicals in the contained product 52.Thus, in the search for a means to protect the foil interface fromattack by the components of the product, various materials were added tothe base prior art sheet material shown in FIG. 1A for the purpose ofproviding a barrier functional for the protective purpose intended.

Since it had been discovered that EVOH by itself serves as a functionalbarrier to the transmission of methyl salicylate, an initial attempt wasmade to provide a layer of EVOH between the metal foil layer 12 and theproduct. To this end a five layer film, coextruded by the castcoextrusion process, was laminated to the inner layer (22 of the basesheet structure represented by the prior art structure of FIG. 1A). Thecoextruded film which was laminated at layer 22 was as follows:

    EAA/ADH/EVOH/ADH/LLDPE                                     (Experiment W)

The adhesive on both sides of the EVOH was Admer NF-500, an anhydridemodified adhesive material based on LLDPE. The EVOH had a vinyl alcoholcontent of 66 mole percent. The five layer coextruded film was 0.09 mm.thick. The EAA layer of the five layer coextruded film was bonded to theEAA layer corresponding to layer 22 in FIGS. 1 and 1A. This filmprovided good adhesion at the foil layer, with fair adhesion between theEVOH layer 14 and the adhesive layers. The film delaminated at theEVOH/adhesive interface when methyl salicylate-containing product wasstored in a package made with it. In another variable, an additionallayer of LLDPE was added to the inside surface of the package. Thisstructure, too, was not able to hold the methyl salicylate-containingproduct.

In another series of tests, oriented polyester was incorporated into thefilm in combination with the EVOH coextrusion. In this experiment, theEAA layer 22 was omitted. A layer of oriented polyester 0.012 mm thickwas adhesive laminated directly to layer 12 of the foil using polyesterurethane curing adhesive. The same five layer coextruded film was thenadhesively laminated to the polyester using a second polyester urethanecuring adhesive. Finally a layer of EAA was attached to the LLDPEsurface of the coextruded film to complete the sheet structure for thetrials. The final structure of the sheet material was as follows:##STR1## A second, similar structure was made using a third polyesterurethane curing adhesive, as follows: ##STR2## These materials alsofailed to successfully hold the methyl salicylate product.

While the initial testing of EVOH had indicated that it provided a goodbarrier to transmission of methyl salicylate, the initial attempts toincorporate EVOH into the sheet material and thereby provide functionalprotection for the foil layer 12 had failed to live up to theirexpectations. Thus the pursuit of the solution then headed in adirection away from EVOH. Additional sheet materials were made withpolyester, which had also, in separate tests, shown a good barrierproperty for methyl salicylate. These too failed. Attempts were madewith certain epoxies. These too failed.

Improvement was finally obtained with a coextruded structure fabricatedby the tubular water quench coextrusion process. The structure was 0.09mm. thick, and was arranged as follows:

    LDPE/Adh 220/EVOH/Adh 220/LLDPE                            (Experiment AW)

The LDPE and EVOH layers were each 20% of the thickness. The twoadhesive layers were each 10% of the thickness. The LLDPE layer was 40%of the thickness. The adhesive 220 was a low density polyethylene basedadhesive containing about of 0.14% maleic anhydride, according to themanufacturer.

After storage testing with a methyl salicylate product, the packagingmaterial had a peel strength of about 335 grams per cm. width.

A still strong packaging structure was made using the following fivelayer structure, coextruded by the tubular water quench process.

    LDPE/Adh 550/EVOH/Adh 550/LLDPE.                           (Experiment AX)

The overall 5-layer structure was 0.09 mm. thick. The LLDPE was about40% of the thickness. The EVOH and LDPE were each about 20%, and theAdh. 550 layers were each about 10%. These five layers represent layers24 (LDPE), 20, 14, 18, and 16, respectively and in order, in FIG. 1. TheLDPE side of the coextruded film was corona treated in line with thecoextrusion process, and was subsequently extrusion laminated to thefoil using EAA layer 22 0.05 mm. thick as the laminant.

Tubes were made with this sheet structure, filled with productcontaining methyl salicylate and storage tested for up to 3 months at upto 49° C. The tubes were 1.9 cm. diameter, 6.7 cm. in length. The tubeswere tested periodically, and at the end of the test, for interlayeradhesion, and for seal integrity along longitudinal lap seam 50. Thetesting showed that the lap seam remained in good condition, and thesheet material could not be separated at any interface between the foillayer 12 and the product contact LLDPE layer 16.

Experiment AX was repeated as Experiment "AX-2" but the corona treatmentwas done out-of-line between the extrusion fabrication process and theextrusion lamination process.

Additional experiments were then conducted to further define theinvention. Five layer structures representing layers 24, 20, 14, 18, and16 were coextruded, with the same thicknesses as in Experiment AX,except as noted, in an air quenched tubular coextrusion process,generally described as "blown extrusion." Table 1 shows these additionalstructures, with processing and structural differences indicated.

Each 5-layer coextruded structure was extrusion laminated to the basesheet as illustrated in FIG. 1, using 0.05 mm. of EAA as the extrusionlaminant, except as noted, all as previously described for ExperimentAX. The base sheets in Experiments W, AT, and AU differed slightly fromthe others, but the differences were inconsequential to the results ofthe experimental testing for peel strength and lap seam integrity. Thelaminated base sheets were formed into lap seamed tubes as in FIGS. 1and 3. Samples of the tubes filled with the methyl salicylate productwere stored at different temperatures, typically 23° C., 41° C., and 49°C. The tubes were examined periodically for interfacial adhesion and lapseam integrity. Table 1 shows the results of the most severe test,namely at 49° C., except for Experiment AX-2 which represents 41° C.storage.

                                      TABLE 1                                     __________________________________________________________________________                                                     Test Results after                                                            Storage at                                   Maleic                           49° C. for Period                                                      Indicated                                    anhydride  Corona                                                                             Corona           Peel Strength                Coex-           in    Ethylene                                                                           Treat-                                                                             Treatment        Instron,                     trusion         Adhesive                                                                            Content                                                                            ment at               grams/cm ·                                                           width    Lap                 Experi-                                                                           Pro-                                                                              Coextruded                                                                            Layers                                                                              in   In-Line,                                                                           Extrusion        2  3  4  Seam                ment                                                                              cess                                                                              Structure                                                                             18 and 20                                                                           EVOH Dynes                                                                              Laminator                                                                           Comments   mths                                                                             mths                                                                             mths                                                                             Integrity           __________________________________________________________________________    W   cast                                                                               ##STR3##                                                                             0.13% 34%  yes  unknown          D  -- -- --                  AT  TWQ                                                                                ##STR4##                                                                             0.14% 38%  yes  unknown                                                                             Foil staining  after 31/2 months                                              storage    -- -- -- satis- factory      AU  TWQ                                                                                ##STR5##                                                                             0.14% 38%  yes  unknown                                                                             Extrusion laminant was coextrusion                                            of .038 mm. LDPE and 0.013 mm. EAA,                                           with EAA toward the foil. staining                                            after 31/2 months                                                                        --orage.                                                                         -- -- satis- factory      AW  TWQ                                                                                ##STR6##                                                                             0.14% 38%  yes  yes              NM NM 335                                                                              good                AX  TWQ                                                                                ##STR7##                                                                             0.32% 38%  yes  yes   Peel Strength CN5 at both 6 weeks                                             and 3 months                                                                             NM CN5                                                                              NM good                AX-2                                                                              TWQ Same as AX                                                                            0.32% 38%  no   no    Corona treated to                                                                        NM 236                                                                              NM                                                           42 dynes, out of line,                                                        between extrusion                                                             process and extrusion                                                         laminating process.                                                           Storage for test                                                              purposes was at 41° C.           AZ  Blown                                                                             Same as AX                                                                            0.32% 38%  38   yes              441                                                                              NM 268                                                                              good                BA  Blown                                                                             Same as AX                                                                            0.32% 38%  38   no               504                                                                              NM 311                                                                              good                BB  Blown                                                                             Same as AX                                                                            0.32% 38%  no   yes              331                                                                              NM 181                                                                              good                BC  Blown                                                                              ##STR8##                                                                             0.13% 38%  38   yes              382                                                                              NM 260                                                                              good                BD  Blown                                                                              ##STR9##                                                                             0.32% 38%  40   yes              445                                                                              NM 283                                                                              good                BE  Blown                                                                              ##STR10##                                                                            0.32% 38%  41   yes   Same as BD, except EVOH layer was                                             10% of thickness. LDPE Layer was                                              25% and LLDPE was                                                                        409.                                                                             NM 205                                                                              good                BF  Blown                                                                              ##STR11##                                                                            0.32% 38%  41   yes   Same as BD, except EVOH layer was                                             30% of thickness. LDPE layer was                                              15%, and LLDPE layer                                                                     350 35%.                                                                         NM 228                                                                              good                BG  Blown                                                                              ##STR12##                                                                            0.32% 29%  40   yes              335                                                                              NM 268                                                                              good                __________________________________________________________________________     D = Delaminated                                                               NM = Not Measured                                                             LDPE and LLDPE are from Dow Chemical Company except as noted                  LDPE-EX and LLDPEEX are from Exxon Chemical Company                           TWQ = tubular water quench                                                    Adh 220 has a low density polyethylene base resin.                            Adh 500 and 550 have linear low density polyethylene base resins.             CNS = CANNOT SEPARATE                                                    

The coextruded film can be as little as about 0.035 mm. thick, up toabout 3 mm. thick, with a preferred range of about 0.05 mm. to about0.75 mm. Flexible films are preferably up to about 0.25 mm. or 0.30 mm.thick.

The maleic anhydride content as reported herein is determined usingFourier Transform Infrared Spectroscopy. Samples are prepared bypressing the polymer pellets at 190° C. and 4000 psi for 2 minutes toproduce a film approximately 0.15 mm. thick. The infrared spectrum inthe region around 1790 cm⁻¹ is measured for each film and the absorbanceof the 1790 band is recorded. The thickness of each sample film ismeasured and the ratio of absorbance at 1790 to thickness of the film iscompared to a calibration curve produced using maleic anhydridestandards.

Throughout this teaching, the anhydride content is taught in terms ofthe maleic anhydride content, since the preferred anhydride is maleicanhydride. It is contemplated that other anhydrides will functionsimilar to maleic anhydride, so long as the layer composition containsan amount of active anhydride which is equivalent to the amount ofanhydride contained in the recited amounts of maleic anhydride.

Sheet materials of the invention are capable of holding productscontaining active carboxy or sulfoxy groups, such as methyl salicylate,acetic anhydride, acetone, undecylenic acid, ichthamnol, andpolyurethane prepolymers.

The fabrication of the sheet material of FIG. 1 requires some laminatingprocessing. However, to the extent coextrusion processing can be used,the cost of the fabrication can be minimized. It is seen to beespecially desirable to coextrude the 5-layer substructure comprisinglayers 14, 16, 18, 20, and 24. The specific materials for the severallayers are chosen, within the family of resins disclosed for eachrecited layer, such that they will have rheological propertiescompatible with the coextrusion process. In that regard, it is desirablethat the compositions of adhesive layers 18 and 20 have melt indexes, at210° C., of between 3 and 9, preferably between 5 and 7.

A preferred process for coextrusion of the 5-layer substructure is aliquid quench coextrusion process, and preferably tubular water quench.The quench water temperature may be as high as 60° C., but is preferablylower, such as 30°-35° C.

Another, less preferred, process is the blown tubular coextrusionprocess wherein the extrudate is cooled by a gaseous medium such as roomtemperature air.

The outer surface of the LDPE layer which is to become layer 24 in theassembled sheet material is preferably corona treated in line with thecoextrusion process, to a level of about 42-48 dynes. The sheet materialof FIG. 1 is then assembled by lamination of the 5-layer coextruded filmto the previously formed laminate (as seen in FIG. 1A) by combining thetwo subassemblies by heat and pressure in a hot nip.

In a less preferred process variation, the corona treatment may beomitted at the coextrusion step, and performed at another time prior tolamination, such as in-line with the hot nip lamination. However, thistreatment process is less efficient than the preferred in-line treatmentat the coextrusion step.

The EVOH of layer 14 has an ethylene content of no more than 45%,preferably at least 28%, most preferably at least 32%. While higherlevels of ethylene in the EVOH make the composition more flexible andpliable, at least a part of the barrier property appears to be providedby the vinyl alcohol content, and thus at least 55% vinyl alcohol ispreferred with a maximum vinyl alcohol content of about 72%, preferablyabout 64%, such that the EVOH composition will have facileprocessability in the extrusion process. Layer 20 is an adhesivecomposition having the capability to adhere EVOH layer 14 to LDPE layer24. While it is desirable to have the composition of layer 20 be thesame as the composition of layer 18, and same is most economical inprovision of coextruded films as shown in FIG. 5, adhesive layer 20 maybe selected to have a different composition. For example, adhesive layer20 may have a lower anhydride modification level than layer 18, or itmay have a different base resin composition such as LDPE, and especiallydifferent rheological properties, in order to improve its adhesion tolayer 24.

Layer 26 is a primer which is applied to foil layer 12 in order toenhance the adhesion of the foil to the coextruded film. A preferredprimer is the conventionally known chromium complexed polyacrylic acidprimer. The EAA layer 22 serves the primary adhesion function betweenfoil layer 12 (through primer layer 26) and LDPE layer 24 of the fivelayer coextruded film.

Referring now to the layers on the outside of the sheet structure fromfoil layer 12, and namely those layers between foil layer 12 and LDPElayer 32. While those layers are conventional in that they are used asthe outer layers in conventional sheet materials used for makingsqueezable tubes, discussion of their purpose and function will aid inunderstanding the overall sheet structures of the preferred embodiments.Layer 28 provides an adhesive function to the foil similar to that oflayer 22. LDPE layer 30 provides an adhesive function between layer 28and paper layer 36, through PEI primer layer 38. PEI primer layer 40 isalso functional in providing enhanced adhesion between paper layer 36and LDPE layer 34. Typically, layer 34 is pigmented in order to give adesired color and appearance to the outer surface of the package.Finally, LDPE layer 32 is clear and provides the outer and glossysurface of the package.

The outer composite substructure, between layers 28 and 32, providesbulk, appearance, protection of foil layer 12 from physical abuse, andmay provide some stiffness or other desirable physical properties to thepackage. Thus the substructure, including layers 30 and 32, and all thelayers in between, could be replaced with other materials comprising oneor more layers which provide the desirable functions and properties forthe specific product application contemplated.

Turning now to FIGS. 2-4, it is seen that the sheet material shown inFIG. 1 may be used in fabrication of a tube having a lap seam 50extending longitudinally along its length. The lap seam is formed byfolding a portion of the sheet material onto itself such that a portionof an outside surface layer 32 on an underlying edge of the sheetmaterial is in facing relationship with a portion of an inside surfacelayer 16 on an overlying portion of the sheet material at the locationwhich forms the lap seam 50. The facing portions of the sheet materialare then heated and pressed together such that the polymeric materialsin the facing portions flow and bond to form the desired lap seam 50 asshown.

FIG. 4 shows the cross section of another exemplary package made usingsheet materials of the invention. In this embodiment of the packages ofthe invention, portions of the sheet material 10 are brought into facingrelationship to each other with the layer 16 of the corresponding facingportions toward the inside of the enclosure. Heat seals are thenfabricated about contiguous portions of the facing portions of the sheetmaterial to make the indicated fin seals 54 seen at FIG. 4.

FIG. 5 shows a less complex embodiment of the invention. This embodimentof the invention is useful where the extremely high barrier propertiesof the foil layer are not necessarily needed. Without the requirementfor the foil layer, it is seen that the sheet material can besubstantially less complex. Indeed, if covering layer 519 is polymeric,it is possible to make the sheet material at FIG. 5 by a one stepprocess of coextrusion.

The functional barrier properties of the sheet material of FIG. 5 aregenerally provided by the EVOH layer 514, especially concerning barriersto transmission of oxygen and methyl salicylate. Layer 516 provides asubstantial barrier to the transmission of moisture, having a moisturevapor transmission rate of no more than about 0.9 grams/645 cm² -24hours at 100% relative humidity. The composition of layer 516, as inlayer 16, is preferably based on an olefin polymer or copolymer. Apreferred olefin is an ethylene, as polymer or copolymer, but thecomposition may, alternatively, be based on propylene, butylene(including polyisobutylene) or a combination of the above; or otheralpha olefins having a primary monomer containing at least three carbonatoms.

The composition of covering layer 519 may be selected with respect toits capability to serve as a barrier to transmission of a selectedmaterial. Its primary function, however, is usually that of protectingEVOH layer 514 from physical abuse when it is used as the outside layerof the package, and from physical attack by the components of theproduct when it is used toward the inside of the package from layer 514.Indeed, covering layer 519 may include a multiple layer structureincluding another adhesive layer, such as an adhesive polyethylene,especially a linear low density polyethylene, containing at least about0.10%, preferably at least about 0.13%, most preferably at least about0.20% maleic anhydride equivalent, adjacent EVOH layer 514, whichrepresents the same anhydride criteria as for layers 18, 518, and 20.519 may include other layers of materials which serve to protect ormodify, or otherwise enhance, or make more effective, the properties ofthe EVOH. To that end, and especially with respect to using layer 516toward the inside of the package, the sheet material of FIG. 5 is seento be useful for packaging a variety of products which benefit from thebarrier properties of EVOH, yet require substantial levels of adhesionbetween adhesive layer 518 and EVOH layer 514.

For purposes of this invention, it is necessary that the EVOH have avinyl alcohol content of at least 55%, preferably at least 60%, in orderto provide the primary barrier property to impede the transmission ofthe methyl salicylate product toward foil layer 12.

It is seen from the previous discussion that adhesive layer 18 includesa chemically modifying component of anhydride for provision of chemicalbonding to the EVOH. It may also incorporate therein a material whichprovides for physical bonding as by a tackifying resin, such as one ofthe elastomers, which provides for a physical bonding property throughtackiness. Typical of elastomers which may be incorporated into layer 18are polyisobutylene, one of the styrene-blocked olefin copolymers suchas styrene butadiene styrene copolymer or styrene ethylene butylenestyrene copolymer, one of the diene modified olefins or rubbers such asethylene propylene diene monomer terpolymer, an ethylene propylenecopolymer such as ethylene propylene rubber, or the like. While lowlevels of elastomer additive will provide an advantage in some cases,usually 3% to 5% additive is needed in order to provide a discerniblefunctional improvement. And while up to 25% additive may be used in somecases, usually there is no advantage in using more than 15%, so that isnormally a practical upper limit. Layer 20 may be likewise modified.

Most preferred anhydride levels are about 0.26% to about 0.40%. Levelsof 0.37% to 0.60% are acceptable for layers 18 and 20, but are notespecially preferred. Layer 24 of LDPE is compatible with beingadhesively bonded to layer 22 in an extrusion lamination process, aswell as to bonding to the adhesive composition of layer 20 in thecoextrusion process. Layers 22 and 24 could be combined, or theircompositions could be changed, so long as they provide the desiredadhesion, or the compatiblization of the adhesiveness between EVOH layer14 and foil layer 12. Thus layer 24 could be EAA instead of thepreferred LDPE, and layer 22 could be EMAA instead of the recited EAA;whereby it is seen that various combinations of materials could providethe desired adhesion.

Thus it is seen that the sheet materials of the invention provide thecapability to package chemically aggressive products, including productscontaining highly volatile components, in flexible tube structures whichare less subject to stress cracking, and are desirable for providingimproved packaging structures. Such products include those containingmethyl salicylate. It is also seen that the invention provides amultiple layer film comprising EVOH which is functional for providing alesser degree of protection, in a much simpler structure, for productswhich are less demanding of the properties of the sheet material, whilestill providing excellent barrier in EVOH layer 514 to transmission ofoxygen or methyl salicylate.

With the sheet materials of the illustrated embodiments having thus beendisclosed, it is seen that several and various modifications may be madeto the invention without departing from the spirit and scope of theconcept. Thus the invention should be interpreted, not only with respectto the illustrated embodiments, but more appropriately in light of theappended claims.

Having thus disclosed the invention, what is claimed is:
 1. A multiplelayer sheet material, comprising:(a) a first layer of metal foil; (b) asecond layer comprising ethylene vinyl alcohol copolymer having a firstsurface disposed toward said foil layer and a second surface disposedaway from said foil layer; and (c) adhesive means between said first andsecond layers, said adhesive means comprising one or more layers havinganhydride content equivalent to between about 0.10% and about 0.60%maleic anhydride.
 2. A multiple layer sheet material as in claim 1wherein said adhesive means comprises a layer having anhydride contentequivalent to between about 0.13% and about 0.40% maleic anhydride.
 3. Amultiple layer sheet material as in claim 1 wherein said adhesive meanscomprises a layer having anhydride content equivalent to between about0.26% and about 0.40% maleic anhydride.
 4. A multiple layer sheetmaterial as in any one of claims 1, 2, or 3, wherein said metal foillayer is adapted to serve as a barrier to transmission of volatileproduct components through said sheet material.
 5. A multiple layersheet material as in claim 1 and including protective means on a firstsurface of said foil layer, said first surface of said foil layer beingdisposed away from said ethylene vinyl alcohol copolymer layer, and acovering layer on said second surface of said ethylene vinyl alcohollayer.
 6. A multiple layer sheet material as in claim 5 and including alayer of adhesive between said second layer and said covering layer andwherein said adhesive means includes a layer of adhesive disposed onsaid first surface of said second ethylene vinyl alcohol layer.
 7. Amultiple layer sheet material as in claim 6 wherein said layer ofadhesive between said second layer and said covering layer comprises abase polymeric resin and anhydride comprising active anhydride componentequivalent to between about 0.13% and about 0.40% maleic anhydride, saidsheet material having interfacial adhesion between the pairs of saidlayers at the interfaces thereof, said sheet material being adapted toprotect the interfacial adhesion between said layer of metal foil andsaid adhesive means from being attacked when the sheet is in the form ofa package, by a packaged product having a component capable of attackingthe interfacial adhesion therebetween, such that a package made withsaid sheet material is adapted to hold the product over the normal shelflife of the product.
 8. A multiple layer sheet material as in claim 7wherein the composition of said adhesive layer between said second layerand said covering layer has a melt index at 210° C., of between 3 and 9.9. A multiple layer sheet material as in claim 6 wherein said ethylenevinyl alcohol in said second layer comprises about 55 mole percent toabout 72 mole percent vinyl alcohol moieties.
 10. A multiple layer sheetmaterial as in claim 9 wherein said layer of adhesive between saidsecond layer and said covering layer comprises a base polymeric resinand anhydride comprising active anhydride component equivalent tobetween about 0.10% and about 0.60% maleic anhydride.
 11. A multiplelayer sheet material as in claim 10 wherein the composition of saidadhesive layer between said second layer and said covering layer has amelt index at 210° C., of between 3 and
 9. 12. A multiple layer sheetmaterial as in claim 6 wherein said layer of adhesive between saidsecond layer and said covering layer comprises a base polymeric resinand anhydride comprising active anhydride component equivalent tobetween about 0.10% and about 0.60% maleic anhydride.
 13. A multiplelayer sheet material as in claim 12 wherein the composition of saidadhesive layer between said second layer and said covering layer has amelt index, at 210° C., of between 3 and
 9. 14. A multiple layer sheetmaterial as in any one of claims 6-8 wherein the composition of saidadhesive layer between said second layer and said covering layerincludes a material which provides for physical bonding properties, inan amount up to 15% by weight.
 15. A multiple layer sheet material as inclaim 6, 9, 12, 7, or 13 wherein the composition of said adhesive layeron said first surface of said second layer comprises the composition ofsaid adhesive layer between said second layer and said covering layer.16. A multiple layer sheet material as in claim 6, 9, 12, 7, or 13wherein the composition of said adhesive layer between said second layerand said covering layer includes a tackifying resin, in an amount up to15% by weight, and wherein the composition of said adhesive layer onsaid first surface of said second layer comprises the composition ofsaid adhesive layer between said second layer and said covering layer.17. A multiple layer sheet material comprising a first layer of ethylenevinyl alcohol copolymer having first and second surfaces, a secondcovering layer on said first surface of said ethylene vinyl alcoholcopolymer layer, an adhesive layer on said second surface of saidethylene vinyl alcohol copolymer layer, said adhesive layer comprisingan ethylene polymer or copolymer component and an anhydride componentcomprising anhydride equivalent to about 0.10% to about 0.60% maleicanhydride, and having a melt index, at 210 degrees C., of between 3 and9, and a layer of linear low density polyethylene on said adhesive layeropposite said first layer, said covering layer comprising low densitypolyethylene.
 18. A multiple layer sheet material as in claim 17 whereinsaid adhesive layer on said second surface of said first layer comprisesanhydride content equivalent to between about 0.13% and about 0.40%maleic anhydride.
 19. A multiple layer sheet material as in claim 17wherein said adhesive layer on said second surface of said first layercomprises anhydride content equivalent to between about 0.26% and about0.40% maleic anhydride.
 20. A multiple layer sheet material comprising afirst layer of ethylene vinyl alcohol copolymer, a covering layer on afirst side of said ethylene vinyl alcohol copolymer layer, a layer of anethylene polymer or copolymer on a second side of said ethylene vinylalcohol copolymer layer, an adhesive layer between said first layer andsaid layer of ethylene polymer or copolymer, the composition of saidadhesive layer between said first layer and said layer of ethylenepolymer or copolymer comprising active anhydride content equivalent tobetween about 0.10% and about 0.60% maleic anhydride.
 21. A multiplelayer sheet material as in claim 20 wherein said adhesive layer betweensaid first layer and said layer of ethylene polymer or copolymercomprises anhydride content equivalent to between about 0.13% and about0.40% maleic anhydride.
 22. A multiple layer sheet material as in claim20 wherein said adhesive layer between said first layer and said layerof ethylene polymer or copolymer comprises anhydride content equivalentto between about 0.26% and about 0.40% maleic anhydride.